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Toxicological Endpoints 

 The endpoints that were used to complete this assessment are summarized in the Table 1 and 

are unchanged from those used in the previous ORE assessment for the RED (D318630). 

Endpoints were selected only for incidental oral and inhalation exposures. No endpoints were 

selected for dermal exposure because no effects were observed at the limit dose in the 21 day 

dermal study in rabbits. The target MOE (i.e. level of concern) for short term inhalation 

exposures is 100. The target MOE for intermediate/long term inhalation exposures is 1000 

because an additional safety factor of 10 is added to account for the lack of a NOAEL. The 

target MOEs for inhalation exposures are the same for both occupational and residential 

exposures. The target MOE for short term incidental oral exposures is 300 which include an 

FPQA database uncertainty factor of 3X to account for the lack of a DNT. The target MOE for 

intermediate/long term incidental oral exposures is 100. 

Table 1 –Endpoints for Assessing Occupational and Residential Risks for Pyrethrins 

Exposure 

Scenario

Dose Used in Risk 

Assessment

Level of Concern (LOC) 

for Risk Assessment

Study and Toxicological Effects

Incidental Oral – 

Short-Term (1-30 days) NOAEL= 20 

mg/kg/day 

Residential MOE = 300 

Occupational MOE= N/A 

Acute neurotoxicity study in rats

LOAEL = 63 mg/kg/day based on tremors in females 

Incidental Oral - 

Intermediate-Term 

(1- 6 months) 

NOAEL= 6.4 

mg/kg/day 

Residential MOE = 100 

Occupational MOE = N/A 

Two generation reproduction study in rats

LOAEL = 65 mg/kg/day based on decreased F1b pup 

body weight/body-weight gain during lactation 

Dermal Exposure - Short, 

Intermediate & Long Term 

No endpoint for this exposure scenario was identified following repeated [21 day] dermal exposure to rabbits 

at the limit dose.

Inhalation - Short-Term NOAEL= 7.67 

mg/kg/day 

[0.03 mL/kg/day] 

Residential MOE = 100 

Occupational MOE = 100 

Subchronic inhalation toxicity study in rats

LOAEL = 25.56 mg/kg/day based on tremors, labored 

breathing, hyperactivity, secretory signs, matted coat, 

decreased body weight/body-weight gain 

 Inhalation - Intermediate & 

Long-Term 

LOAEL= 2.56 

mg/kg/day 

[0.01 mL/kg/day] 

Residential MOE = 1000 

Occupational MOE = 100 

Subchronic inhalation toxicity study in rats

LOAEL = 2.56 mg/kg/day based on respiratory tract 

lesions 

 

Occupational Handler Exposure and Risk 

The occupational handler risks were assessed for the pet spray use using the same exposure data, 

assumptions and calculation methods that were used in the ORE assessment for the RED 

(D316630) with the only difference being the increased application rate. As was done 

previously, only inhalation exposures have been assessed for the occupational handlers applying 

pyrethrin pet sprays. Dermal exposures were not assessed because no dose or endpoints were 

selected for dermal exposure. The MOE for the occupational handler exposure scenario is 

included in Table 1. The short term MOE is above the target MOE of 100 and therefore the short 

term risk is not of concern. The intermediate/long term MOE of 1000 is above the target MOE 

of 1000 and therefore the intermediate/long term risk is not of concern. 

 
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Table 1 - Pyrethrin Inhalation MOEs for Occupational Handlers 

(Pet Groomers and Veterinary Technicians)

Exposure 

Scenario 

Inhalation Unit 

Exposure 

(μg/lb ai) 

Application Rate 

(lb ai/16 oz can) 

Amount 

Ai Used 

Inhalation Dose 

(mg/kg/day) 

Short Term 

MOE 

Intermediate/ 

Long Term MOE 

Aerosol Can 

Application of 

Pet Sprays 

1300 0.002 0.008 lb 0.00015 51,000 17,000 

* Baseline inhalation unit exposures represent no respirator. The unit exposure value is from PHED. 

* The application rate is based on the maximum label rate 0.20 % ai for pet spray uses. 

* The amount ai used is based upon the application of 8 ounces of product applied per animal times 8 animals treated per day. 

* Inhalation dose = [unit exposure value * 0.001 mg/gm * Application rate* Amount Used)] / Body weight (70 kg). 

* MOE = NOAEL/Dose where the NOAEL is 7.67 mg/kg/day for short term exposures and 2.56 mg/kg/day for intermediate/long term exposures. 

* The target MOE is 100 for short term inhalation exposures and 1000 for intermediate/long term inhalation exposures.

 

Occupational Post Application Exposure and Risk 

As was the case for the previous ORE assessment, occupational post application exposures were 

not assessed for pet spray uses because no dermal endpoints were selected. 

Residential Hander Exposure and Risk 

As was the case for the previous ORE assessment, only short term exposures were assessed for 

residential handlers applying pet sprays because the pyrethrins are applied to pets only on an 

intermittent basis. The exposure and risk estimate for the residential handler pet spray scenario 

is included in Table 2. The MOE is greater than the target MOE of 100, therefore the risks are 

not of concern. 

Table 2 - Pyrethrin Inhalation MOE for Residential Handlers 

(Application of Pet Sprays)

Exposure 

Scenario 

Inhalation Unit 

Exposure (μg/lb ai) 

Application Rate 

(lb ai/16 oz can) 

Amount Ai 

Used 

Inhalation 

Dose 

(mg/kg/day) 

Short 

Term 

MOE 

Aerosol Can 

Application of 

Pet Sprays 

1300 0.002 0.001 lb 0.000019 400,000 

* Baseline inhalation unit exposures represent no respirator. The unit exposure value is from PHED. 

* The application rate is based on the corrected value of 0.20 % ai provided by the registrants. 

* The amount ai used is based upon the application of 8 ounces of product applied per animal times 1 animal treated per day. 

* Inhalation dose = [unit exposure value * 0.001 mg/gm * Application rate* Amount Used)] / Body weight (70 kg). 

* MOE = NOAEL/Dose where the NOAEL is 7.67 mg/kg/day for short term exposures. 

* The target MOE is 100 for short term inhalation exposures and 1000 for intermediate/long term inhalation exposures.
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Residential Post Application Exposure and Risk 

The residential post application exposures to toddlers playing with pets after treatment were 

assessed in the same manner as was done in the ORE assessment for the RED (D318630) with 

the only difference being the increased application rate. Only incidental oral exposures were 

assessed because dermal endpoints were not selected. The risk for this scenario is included in 

Table 3. The MOE is greater than the target MOE of 300, therefore the risk is not of concern. 

Table 3 - Pyrethrin Post-application Risk to Toddlers Playing with Pets after Treatment 

with Spray Formulations 

Application 

Method AR (mg ai/cm2

) Transferable Residue 

(mg/cm2) 

Daily Oral Dose 

(mg/kg/day) 

Short Term 

MOE* 

Aerosol Can 0.076 0.015 0.010 2000 

Daily Oral Dose = TR * SEF * SAhands * Freq 

where: AR = Application Rate or amount applied to animal in a single treatment (mg ai/animal) = 

 1⁄2 of 16 oz spray container with maximum of 0.2% ai per 6000 cm2

/animal 

 TR = Transferable Residue (AR * 20%) 

 SApet = Surface Area of a treated dog (6000 cm2

/animal) 

 SEF = Saliva Extraction Factor (50%) 

 SAhands = Surface Area of the hands (20 cm2

) 

 Freq = Hand-to-Mouth Events (1 event/day) 

 BW = 15 kg for toddler 

 

MOE = Short Term Oral NOAEL (20 mg/kg/day)/Daily Oral Dose (mg/kg/day)